Traditionally, patient monitors, such as an EKG sensor, pulse sensor, blood oxygen sensor, and the like are each connected with its control unit by a cable. This maze of cables is inconvenient to set up and uncomfortable for the patient. Moreover, moving the patient typically requires disconnecting the cables and reconnecting them after the move. In addition to the inconvenience, the patient is left unmonitored during the move.
In an effort to eliminate the cables, wireless battery powered sensor devices have been proposed. However, when monitoring patients' vital signs, or dosing a critical medication, a dead battery can be more than inconvenient; it can be life threatening.
Often, a battery operated component is equipped with a sensor that measures the battery's current charge level. Some provide a simple green light for a strong charge and a red light for a weak charge, i.e., the battery is about to run out. Others provide a gauge which indicates the remaining portion of battery life. Battery life gauges merely indicate a level of charge—not when a battery will run out. Nominally similar batteries will hold different amounts of maximum charge or discharge at different rates. As batteries age, they tend to have progressively shorter lives
In a hospital, one patient may have several monitors, perhaps half a dozen or more. With hundreds of patients being monitored, checking the battery status indicators of all the monitors is a logistical nightmare. Thus, on-device battery level monitors do not assure freedom from battery problems in life threatening situations.
Due to these and other problems, system designers have been reluctant to replace standard wired devices with wireless devices when the devices are more critical in nature. If a battery should fail at an inopportune moment, consequences could range from mere annoyances to potentially life threatening situations and malpractice/product liability lawsuits. Nonetheless, some critical devices are equipped with batteries, such as portable respirators and intravenous fluid pumps. Additionally, sometimes non-critical devices are used in a critical situation, such as diagnostic imaging in conjunction with a trauma victim. In an extreme case, if one of these devices should fail due to insufficient battery power, the results could be catastrophic.